local network settings and connection sharing

Hi

I hope this isnt a repeat ask for help but ive had a trawl and cant find anything similar so here goes...

I have 2 PCs both running vista 64 bit that travel in a pair flight cased up. theyre both connected to each other over thier wired network ports to enable the transfer of files between the 2 machines. 1 of the machines now has a wireless adapter fitted to enable me to connect to any wifi thats available (these machines travel around so internet connection is usually wireless and on differing networks).

What Id like to achieve is sharing the internet connection between the 2 machines and still maintain the local network between the 2 machines but I think this is producing some IP conflicts somewhere along the line and the internet connection is therefore very unstable... sometimes its fine on the machine with the wireless card but the 2nd machine wont see the internet connection, other times they both say theyre connected but this doesnt last long.

no amount of ip flushing, renewing or repairing seems to produce a solution and its exhausted my limited knowledge of network settings...

any suggestions anyone? apart from the obvious ditching of vista!! :confused